The present invention relates to a wiring board used for manufacturing a semiconductor device of substantially the same size. The present invention also relates to a method of manufacturing the wiring board and a semiconductor device into which the wiring board is incorporated.
In a chip-size package, the size of which is substantially the same as that of the semiconductor to be incorporated into the package, there is provided an interposer between the semiconductor element and the external connecting terminals such as solder balls. The interposer is provided with wiring for electrically connecting the electrode of the semiconductor element with the external connecting terminals. This interposer is made of flexible material, so that the thermal stress generated by a difference between the coefficient of thermal expansion of the package and that of a mounting board can be reduced.
FIG. 12 is a view showing an example of the conventional BGA (ball grid array) type chip-size package. This semiconductor device is composed in such a manner that a wiring pattern film 14 adheres onto an electrode forming face of a semiconductor element 10 via an elastomer layer 12. The wiring pattern film 14 is supported by an electrically insulating layer 15, and a wiring pattern 16 is formed on the wiring pattern film 14. At one end of the wiring pattern 16, there is provided a lead 20 connected with the electrode 18 of the semiconductor element 10, and at the other end of the wiring pattern 16, there is provided a land 24 which is a part of wiring pattern 16 that is immediately adjacent to, below, and connected with the external connecting terminal 22. In this product, both the elastomer layer 12 and the wiring pattern film 14 become an interposer.
The lead 20 and the electrode 18 are individually connected with each other by the method of lead bonding. The lead 20 is formed crossing a window 26 formed on the wiring pattern film 14. Therefore, the lead 20 is connected with the electrode 18 in the process of lead bonding in such a manner that the lead 20 is cut off by a bonding tool through the window 26.
However, it is not necessarily easy to bond the lead 20 to the electrode 18 with high accuracy by the method of lead bonding. Further, the working efficiency of lead bonding is not necessarily high. In order to overcome the above problems, it is possible to use the method of wire bonding, the working efficiency of which is high, for connecting the wiring pattern 16 with the electrode 18.
However, when wire bonding is conducted on the wiring pattern film 14 supported by the above flexible elastomer layer 12, it is impossible to perform the bonding with high accuracy. The reason for this is as follows. Since the elastomer layer 12 is made of flexible material so as to reduce thermal stress, the pushing force exerted by the bonding tool does not act on the bonding section effectively. Therefore, the bonding wire cannot be assuredly connected.
On the other hand, when the wiring pattern film 14 is made of material the elastic modulus of which is high, instead of the flexible elastomer layer 12, so that the wire bonding property of the wiring pattern 16 can be enhanced, the following problems may be encountered. When the semiconductor device is mounted on a mounting board, thermal stress generated between the mounting board and the semiconductor element 10 acts directly on the external connecting terminals 22. Therefore, an excessively high intensity of stress acts between the external connecting terminal 22 and the mounting board and also between the external connecting terminal 22 and the semiconductor element 10, which could cause of a defective connection.
It is an object of the present invention to provide a semiconductor device in which the electrode of the semiconductor element and the external connecting terminal can be assuredly connected with each other by the method of wire bonding in a semiconductor device including an interposer functioning as a wiring board arranged between the semiconductor element and the external connecting terminal. It is another object of the present invention to provide a wiring board suitably for use in manufacturing the semiconductor device. It is still another object of the present invention to provide a method of manufacturing the semiconductor device.
In order to realize the above objects, the present invention provides a wiring board comprising: a first face joined to an electrode forming face of a semiconductor element; and a second face on the opposite side of the first face, a wiring pattern being formed on the second face, a land joined to an external connecting terminal being formed at one end of the wiring pattern, a wire bonding section connected with a bonding wire being formed at the other end of the wiring pattern, wherein the land is supported by a buffer layer for reducing the thermal stress generated when the semiconductor element to which the wiring board is attached is mounted via the external connecting terminals, and the wire bonding section is supported by a bonding support layer having an elastic modulus capable of allowing wire bonding.
The buffer layer is made of material the Young""s modulus of which is not more than 1 GPa at 30xc2x0 C., and the bonding layer is made of material the Young""s modulus of which is not less than 4 GPa at room temperature.
A plurality of wire bonding sections are arranged in a peripheral section of the second face, and a plurality of lands are arranged inside the region in which the wire bonding sections are arranged. Alternatively, an opening penetrating from the first face to the second face is formed, a plurality of wire bonding sections are arranged in a peripheral section of the opening on the second face, and a plurality of lands are arranged outside the region in which the wire bonding sections are arranged.
The buffer layer and the bonding support layer are supported by a base support layer the elastic modulus of which is the same as that of the bonding support layer, a side of the base support layer composes the first face, and sides of the buffer layer and the bonding support layer compose the second face.
A plane configuration of a wiring pattern formed on the second face is formed into a curve.
The present invention provides a method of manufacturing a wiring board having a first face joined to an electrode forming face of a semiconductor element and also having a second face on the opposite side of the first face, a wiring pattern being formed on the second face, a land joined to an external connecting terminal being formed at one end of the wiring pattern, a wire bonding section connected with a bonding wire being formed at the other end of the wiring pattern, the method of manufacturing the wiring board comprising the steps of: forming a support sheet made of material the elastic modulus of which is so high that it can support bonding in the process of wire bonding, the support sheet partitioning cavities when a partitioning section which becomes a bonding support layer is arranged on one of the faces of the support sheet, forming a buffer layer when cavities are filled with adhesive sheet material by pressing a sheet of metallic foil on a side on which the cavities of the support sheet are formed, via an adhesive sheet made of material capable of reducing the thermal stress caused when the semiconductor element having the wiring board is mounted via the external connecting terminal, making the buffer layer and the bonding support layer adhere onto the sheet of copper foil, and etching the sheet of metallic foil so as to form a wiring pattern on which one end side becomes lands arranged in a region supported by the buffer layer and the other end side becomes a wire bonding section arranged in a region supported by the bonding support layer.
The present invention also provides another method of manufacturing a wiring board having a first face joined to an electrode forming face of a semiconductor element and also having a second face on the opposite side of the first face, a wiring pattern being formed on the second face, a land joined to an external connecting terminal being formed at one end of the wiring pattern, a wire bonding section connected with a bonding wire being formed at the other end of the wiring pattern, the method of manufacturing the wiring board comprising the steps of: forming a support sheet made of material the elastic modulus of which is so high that it can support bonding in the process of wire bonding, the support sheet partitioning cavities when a partitioning section which becomes a bonding support layer is arranged on one of the faces of the support sheet, forming a buffer layer by filling the cavities with material capable of reducing the thermal stress which is caused when the semiconductor element having the wiring board is mounted via the external connecting terminals, so that a surface of the filled material can be the same as the surface of the support sheet; covering the surface of the support sheet on which the buffer layer is formed with a sheet of metallic foil; and etching the sheet of metallic foil so as to form a wiring pattern on which one end side becomes lands arranged in a region supported by the buffer layer and the other end side becomes a wire bonding section arranged in a region supported by the bonding support layer.
The present invention provides a semiconductor device comprising: a semiconductor element on the electrode forming face of which an electrode is formed; a wiring board having a first face joined to an electrode forming face of the semiconductor element and also having a second face on the opposite side of the first face, a wiring pattern being formed on the second face, a land joined to an external connecting terminal being formed at one end of the wiring pattern, a wire bonding section connected with a bonding wire being formed at the other end of the wiring pattern; and a bonding wire for electrically connecting the electrode of the semiconductor element with the wire bonding section of the wiring board, wherein the land is supported by a buffer layer for reducing the thermal stress caused when the semiconductor element having the wiring board is mounted via the external connecting terminal, and the wire bonding section is supported by a bonding support layer the elastic modulus of which is capable of allowing wire bonding.
The present invention also provides a method of manufacturing a semiconductor device comprising the steps of: preparing a semiconductor wafer provided with a plurality of semiconductor elements on the electrode forming faces of which the electrodes are formed; preparing an individual wiring board having a first face joined to the electrode forming face of the semiconductor element and also having a second face arranged on the opposite side to the first face, a wiring pattern being formed on the second face, a land joined to an external connecting terminal being arranged at one end of the wiring pattern, a wire bonding section connected with a bonding wire being arranged at the other end of the wiring pattern; mounting an individual wiring board on the semiconductor wafer corresponding to each semiconductor element so the electrode can be exposed; connecting electrically the electrode with the bonding section of the wiring board by a bonding wire; sealing a region including the electrode, bonding section and bonding wire section with resin; and cutting the semiconductor wafer at a position sealed with the sealing resin along a cutting line between the adjacent semiconductor elements so as to separate it into individual semiconductor elements.
Further, the present invention provides a method of manufacturing a semiconductor device, additionally comprising the step of connecting an external connecting terminal with the land of each wiring board after the process of sealing the electrode, bonding section and bonding wire section with resin.
The present invention provides another method of manufacturing a semiconductor device comprising the steps of: preparing a large size wiring board in which a plurality of openings penetrating from the first face to the second face on the opposite side are arranged in a grid pattern, the individual wiring boards are formed in the periphery of the individual openings, the first face of each wiring board becomes a face joined to the electrode forming face of the semiconductor element, the wiring pattern is formed on the second face, the land connected with the external connecting terminal is provided at one end of the wiring pattern, and the wire bonding section connected with the bonding wire is provided at the other end of the wiring pattern; preparing each semiconductor element, in the central region of the electrode forming face of which the electrode is formed; mounting each semiconductor element on the large size wiring board corresponding to each wiring board so that the electrode can be exposed from the opening; electrically connecting the electrode of the semiconductor element with the bonding section of the wiring board by a bonding wire; sealing a region including the electrode, bonding section and bonding wire section with resin; and cutting the large size wiring board at a position sealed with the sealing resin along a cutting line between the adjacent semiconductor elements so as to separate it into individual semiconductor elements.